Problem: Simplify the following expression: $n = \dfrac{1}{10y} + \dfrac{1}{7y}$
Answer: In order to add expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $10y$ and $7y$ $\lcm(10y, 7y) = 70y$ $ n = \dfrac{7}{7} \cdot \dfrac{1}{10y} + \dfrac{10}{10} \cdot \dfrac{1}{7y} $ $n = \dfrac{7}{70y} + \dfrac{10}{70y}$ $n = \dfrac{7 +10}{70y}$ $n = \dfrac{17}{70y}$